Phenylalanine is an amino acid having the formula C.sub.6 H.sub.5 CH.sub.2 CH--(NH.sub.2)CO.sub.2 H which is considered an essential amino acid in many animals but which can be synthesized by some microorganisms. Escherichia coli is a microorganism which it has been known for some time is capable of synthesizing phenylalanine.
In the wild type organism only enough phenylalanine is produced to satisfy the organisms own requirements. There is insufficient phenylalanine excreted by the wild type organism to be detectable by normal analytical techniques.
Escherichia coli produces phenylalanine using a biosynthetic pathway which starts with a suitable carbohydrate and converts that into intermediaries including erythrose 4-phosphate and phosphoenolpyruvate. These intermediaries are then converted to 3-deoxy-D-arabinoheptulosonate 7-phosphate (DAHP) by an enzyme known as DAHP synthase. The DAHP is in turn converted through a number of steps including the formation of shikimate, to chorismate. The chorismate is then converted through a terminal pathway to phenylalanine.
FIG. 1 attached hereto shows the three main factors affecting the overall conversion of erythrose 4-phosphate and phosphoenolpyruvate to phenylalanine. Firstly, several enzymes of the common pathway of aromatic biosynthesis leading to chorismate, and enzymes of the phenylalanine terminal pathway which branches from chorismate, are sensitive to repression (R) of enzyme synthesis. Secondly, both DAHP synthase isoenzymes at the start of the common pathway and chorismate mutase P-prephenate dehydratase (CMP-PDH) at the start of the phenylalanine pathway are sensitive to feedback inhibition (I). Thirdly, but less importantly, chorismate may be diverted down pathways other than the phenylalanine pathway.